This invention relates to endoprosthesis devices, generally called stents, and, more particularly, to radiopaque markers for use with endoprosthesis devices.
Stents are generally tubular shaped devices that function to hold open a segment of a blood vessel or other anatomical lumen and are useful in the treatment of atherosclerotic stenoses in blood vessels. Stents are particularly suitable for use in supporting and holding back a dissected arterial lining that can occlude the fluid passageway therethrough.
Structures used as stents or intraluminal vascular grafts include coiled stainless steel springs; helical wound spring coil made from shape memory alloy; expanding metal stents formed in a zig-zag pattern; diamond shaped, rectangular shaped, and other mesh and non-mesh designs. Some of the stents currently available employ a self expanding concept, whereby stent expansion is primarily achieved by removing a restraint mechanism holding the stent in a constricted configuration. Other stents in the prior art are delivered to the site by a balloon catheter system, and primarily employ balloon dilation to achieve proper stent expansion.
To accomplish precise placement of stents, various means are employed for identifying the position of the stent within a blood vessel. One means used for accomplishing precise placement of a stent is the attachment to the stent of radiopaque markers so that, through the use of fluoroscopy, the position of the stent within a blood vessel can be identified. Once the stent with its radiopaque markers has been implanted, identification of the stent position during subsequent checkups of the treated segment is easily accomplished because the markers remain visible under fluoroscopy.
In European patent application No. 95302708, assigned to ACS, Inc., a method of coating the stent edges as markers is described. However, this method has several practical disadvantages. First, heavy coating of radiopaque markers onto a stent is somewhat difficult to accomplish. In addition, the radiopaque material might not be attached properly to the stent material and may detach, leaving no way of identifying the position of the stent within the blood vessel. Furthermore, the radiopaque coating may increase the rigidity of the stent, thereby making proper placement difficult and decreasing the stent""s effectiveness.
In another method for enabling the precise identification of a stent location using radiopaque markers, commonly assigned U.S. patent application Ser. No. 08/394,799, filed Feb. 27, 1995, discloses a hollow stent having radiopaque material inserted within the hollow stent wire. Because this method of providing radiopaque marking requires that the stent wire is hollow, this method might not be useful where a hollow stent is not desirable.
Another well-known method for enabling the precise identification of a stent location within a blood vessel is producing the stent itself from a radiopaque material such as tantalum. However, a disadvantage of this method is that tantalum is a relatively soft material and it is, therefore, necessary to use more of this metal to achieve sufficient support from the stent.
It is an object of the invention to provide improved stents.
It is also an object of the invention to provide stents having radiopaque markers.
It is a further object of the invention to provide stents where the distal ends of the stents comprise rivets of material that is more radiopaque than the material from which the stents are made.
These and other objects of the invention will become more apparent in the discussion below.
The radiopaque markers described below are designed for stents produced from a material that is not sufficiently radiopaque to be seen through the use of fluoroscopy, e.g., a material such as Stainless Steel 316L or nitinol. In order to identify the position of the stent during its insertion into the body and after it has been implanted, however, it is enough to mark the stent edges so that they may be seen under X-ray. The location of the stent will thus be evident based upon the pinpoint locations of its two ends.
According to this invention the edges of the stents are marked by inserting rivets through the ends or edges of the stents, which rivets are made of a material that is more radiopaque than the stent material. For example, if the stent material is S.S. 316L, the rivets can be made of gold, tantalum or platinum.